Comparison of prostate contours between conventional stepping transverse imaging and Twister-based sagittal imaging in permanent interstitial prostate brachytherapy.

PURPOSE: To compare prostate contours on conventional stepping transverse image acquisitions with those on twister-based sagittal image acquisitions. MATERIAL AND METHODS: Twenty prostate cancer patients who were planned to have permanent interstitial prostate brachytherapy were prospectively accrued. A transrectal ultrasonography probe was inserted, with the patient in lithotomy position. Transverse images were obtained with stepping movement of the transverse transducer. In the same patient, sagittal images were also obtained through rotation of the sagittal transducer using the "Twister" mode. The differences of prostate size among the two types of image acquisitions were compared. The relationships among the difference of the two types of image acquisitions, dose-volume histogram (DVH) parameters on the post-implant computed tomography (CT) analysis, as well as other factors were analyzed. RESULTS: The sagittal image acquisitions showed a larger prostate size compared to the transverse image acquisitions especially in the anterior-posterior (AP) direction (p < 0.05). Interestingly, relative size of prostate apex in AP direction in sagittal image acquisitions compared to that in transverse image acquisitions was correlated to DVH parameters such as D90 (R = 0.518, p = 0.019), and V100 (R = 0.598, p = 0.005). CONCLUSIONS: There were small but significant differences in the prostate contours between the transverse and the sagittal planning image acquisitions. Furthermore, our study suggested that the differences between the two types of image acquisitions might correlated to dosimetric results on CT analysis.